Delivery device usable in laser peening operation, and associated method

ABSTRACT

A delivery device that is usable in a laser peening operation emits a columnar flow of a fluid that contains therein a beam of electromagnetic energy. The beam is retained within the interior of the flow of fluid since the total internal reflectivity of the flow is sufficient to do so. The flow of fluid that serves as a conduit for the beam also itself impinges on a workpiece and thus contains and washes away the plasma that forms from a laser peening operation, and this resists the plasma from reaching and possibly damaging the delivery device. The carrying of the beam in the columnar flow of fluid avoids the need to maintain a fixed distance between the delivery device and the workpiece, which simplifies the movement by a robotic manipulator of the delivery device along a non-planar surface of a workpiece during a laser peening operation.

CROSS-REFERENCE TO RELATED APPLICATION

The instant application claims priority under 35 U.S.C. § 120 frompreviously co-pending U.S. patent application Ser. No. 15/150,672 filedMay 10, 2016, which in turn claims the benefit of U.S. ProvisionalPatent Application Ser. No. 62/159,399 filed May 11, 2015, thedisclosures of each of which are incorporated herein by reference. Sincethe instant application was filed, U.S. patent application Ser. No.15/150,672 issued as U.S. Pat. No. 10,655,191 on May 19, 2020.

BACKGROUND OF THE INVENTION Field

The disclosed and claimed concept relates generally to a laser peeningoperation and, more particularly, to a method of delivering a beam ofelectromagnetic energy such as a laser beam onto a workpiece.

Related Art

Laser peening is well understood in the relevant art and is usable tointroduce compressive surface stresses into a workpiece. The typicallaser peening operation involves impinging a pulsed high energy laserbeam on a workpiece. The workpiece typically must have an ablative layersituated on it. However, it is also possible to perform laser peeningwithout an ablative layer by ablating the surface of the workpieceitself under a covering of water, sometimes referred to as a waterblanket, with the water being employed to retain by inertial confinementa plasma pressure shock that is created from the laser impinging on theworkpiece. The laser and the related equipment must be spaced apredetermined distance away from the workpiece, typically severalcentimeters or more, because the laser peening operation results in theaforementioned plasma pressure shock wave. The shock wave emanates fromthe location on the workpiece where the laser peening operation is beingperformed, and it is thus desirable to avoid damage to the equipmentfrom the shock wave, both by providing the water blanket and by spacingthe equipment from the workpiece.

While such laser peening equipment and methods have been generallyeffective for their intended purposes, they have not been withoutlimitation. To be effective, the laser must be focused onto a small areaon the workpiece, and maintaining such a focus makes the design andmotion of the robotic laser manipulation and delivery system verycomplex when applied to non-planar surfaces of the workpiece. The amountof water that typically is required in a laser peening operation issignificant because the water delivery mechanism typically coats a largeregion of the workpiece in a water blanket. Such water must be collectedand drained or otherwise removed from the work site, which can betedious and costly. Alternatively, the laser peening operation can takeplace with the workpiece being submerged in water, which includes itsown complications and expense. Improvements would therefore bedesirable.

SUMMARY

Accordingly, an improved delivery device that is usable in a laserpeening operation emits a columnar flow of a fluid that contains thereina beam of electromagnetic energy. The beam is retained within theinterior of the flow of fluid since the total internal reflectivity ofthe flow is sufficient to do so. The flow of fluid thus effectivelyfunctions in the same fashion as fiber optic cable in that it containstherein the beam of electromagnetic energy based upon its having asufficiently high total internal reflectivity. The flow of fluid thatserves as a conduit for the beam also itself impinges on the workpieceand thus blankets the plasma and washes away the debris that fauns froma laser peening operation. Additional water to form a water blanket onthe workpiece is thus unnecessary and makes an improved method of usingthe delivery device practical for a laser peening operation and forother applications.

Accordingly, an aspect of the disclosed and claimed concept is toprovide an improved delivery device that outputs a columnar flow offluid that has a beam of electromagnetic energy contained therein basedupon the total internal reflectivity of the flow.

Another aspect of the disclosed and claimed concept is to provide animproved method of performing a laser peening operation by using such adelivery device.

Another aspect of the disclosed and claimed concept is to provide animproved delivery device and method of use that enable a laser peeningoperation to be performed on a workpiece without additionally needing awater blanket on the workpiece.

Another aspect of the disclosed and claimed concept is to provide animproved delivery device that outputs a flow of a fluid that impinges ona workpiece during a laser peening operation and that delivers a laserbeam onto a small spot on the workpiece over a wide range of distancesfrom the delivery device.

Accordingly, an aspect of the disclosed and claimed concept is toprovide an improved delivery device, the general nature of which can bestated as including a housing having a hollow cavity formed therein, aninlet in fluid communication with the cavity and structured to deliver astream of a fluid to the cavity, an outlet in fluid communication withthe cavity and structured to deliver a flow of the fluid out of thecavity, and a delivery mechanism structured to deliver a beam ofelectromagnetic energy out of the outlet and within the flow.

Another aspect of the disclosed and claimed concept is to provide animproved method of employing the aforementioned delivery device. Themethod can be generally stated as including forming within a mediumhaving a first index of refraction a flow of a fluid having a secondindex of refraction, the second index of refraction being greater thanthe first index of refraction, receiving a beam of electromagneticenergy within the interior of the flow, and maintaining a total internalreflectivity inside the flow sufficient to retain the beam within theinterior of the flow.

Optionally, the method can also include impinging the flow and the beamonto a workpiece. Optionally, the method can additionally includeperforming a laser peening operation on the workpiece. Optionally, themethod can further include employing the flow to contain a plasma thatis created from the laser peening operation and to resist the plasmafrom expanding and traveling in a direction generally toward thedelivery device.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the disclosed and claimed concept can begained from the following Description when read in conjunction with theaccompanying drawings in which:

FIG. 1 is a side view, partially cut away, of an improved deliverydevice in accordance with the disclosed and claimed concept;

FIG. 2 is an enlarged view of the indicated portion of FIG. 1; and

FIG. 3 is a flowchart depicting certain aspects of an improved method inaccordance with the disclosed and claimed concept.

Similar numerals refer to similar parts throughout the Specification.

DESCRIPTION

An improved delivery device 4 in accordance with the disclosed andclaimed concept is depicted in FIGS. 1 and 2 in a partially cut awayfashion. The delivery device 4 is usable with a laser 8 which serves asan emitter of electromagnetic energy in order to perform an operation,such as a laser peening operation that is performed on a workpiece 12.While the delivery device 4 is described herein in terms of itsexemplary possible use in the performance of a laser peening operation,it is understood that the ideas contained herein can be used in fashionsother than in connection with a laser peening operation, and it istherefore understood that the laser peening operation that is describedherein is exemplary only and is not intended to be limiting.

The delivery device 4 can be said to include a housing 16 and a deliverymechanism 18. The housing 16 is formed from an appropriate material suchas a metal or a polymer or other material and has a hollow cavity 20formed therein. The housing 16 additionally has an inlet 24 and anoutlet 28 that are both in fluid communication with the cavity 20. Theinlet 24 is in fluid communication with a fluid source 30 which, in thedepicted exemplary embodiment, is a source of a fluid in the form ofreasonably purified liquid water, meaning water that has been filteredand/or otherwise treated, but it is not necessarily intended to refer toa source of water from which all impurities have been removed. While theexemplary fluid that is described herein is liquid water, it isunderstood that other fluids in a liquid state can be employed withoutdeparting from the spirit of the instant disclosure.

The fluid source 30 delivers a stream 34 of the fluid through the inlet24, as is indicated with the arrow 26, and into the cavity 20. The fluidwithin the cavity 20 flows, as is indicated at the arrows 31, toward theoutlet 28, after which the fluid foal's a flow 38 of the fluid as itexits the cavity 20 out of the outlet 28. The housing 16 furtherincludes a nozzle 32 within which the outlet 28 is formed and that formsthe flow 38.

The delivery mechanism 18 can be said to include the laser 8 and canadditionally be said to include a lens 40 that is mounted in an opening36 that is formed in the housing 16. As can be seen in FIGS. 1 and 2,the laser 8 emits a collimated laser beam 44 which impinges a firstsurface 42 of the lens 40. The electromagnetic energy from thecollimated laser beam 44 passes through the lens 40 and out of a secondsurface 46 of the lens 40. The electromagnetic energy from thecollimated laser beam 44 exiting the second surface 46 is caused by thelens 40 to converge through a convergence region 48 into a focal point52 that is depicted in FIG. 2 as being situated within the outlet 28.

It is understood that the exemplary lens 40 is formed of glass or othertransparent solid and is designed to have optical properties that causethe electromagnetic energy of the collimated laser beam 44 to convergeat the focal point 52 based at least in part upon the index ofrefraction of the glass from which the lens 40 is fowled and the indexof refraction of the fluid from the fluid source 30. That is, thecollimated laser beam 44 in the depicted exemplary embodiment isdepicted in FIG. 1 as traveling through a medium 68 which in thedepicted exemplary embodiment is air, and the collimated laser beam 44thus impinges on the lens 40 at an exemplary air-to-glass interface atthe first surface 42. However, at the second surface 46 theelectromagnetic energy exits the lens 40 at an exemplary glass-to-waterinterface. It is understood that water has an exemplary index ofrefraction greater than that of air, and such factors are taken intoaccount when developing the optical parameters of the lens 40.

As can be understood from FIG. 1, the fluid travels as the stream 34through the inlet 24 and into the cavity 20, and the fluid thereafterexits the cavity 20 and travels as the flow 38 into the outlet 28 of thenozzle 32. At least a portion of the flow 38 is, in the depictedexemplary embodiment, a free columnar jet 64 of the fluid and issituated in the medium 68 which, in the depicted exemplary embodiment,is air.

As is best shown in FIG. 2, the outlet 28 can be said to include acurved entryway 50 adjacent a tapered region 54. The outlet 28 in thedepicted exemplary embodiment further includes a straight section 58 ofan unvarying diameter (i.e., transverse to the direction of flow) and ofa length 62. The fluid enters the outlet 28 at the curved entryway 50,which provides a smooth, i.e., non-turbulent, transition from theadjacent cavity 20. The fluid thereafter flows into the tapered region54 which amplifies the fluid velocity while retaining fluid symmetry andnon-turbulence. The fluid then flows into an entrance 56 to the straightsection 58 and then out of an exit 60 of the straight section 58, atwhich time the flow 38 forms the free jet 64. The length 62 of thestraight section 58 provides the final collimation for the fluid stream.

To avoid loss of energy and coherence of the electromagnetic energy thatis output from the laser 8, the laser 8 is focused to avoid impinging onthe nozzle 32 within the outlet 28. This is accomplished, in thedepicted exemplary embodiment, by setting the focal point 52 of theelectromagnetic energy from the laser 8 at a location approximatelymidway along length of the straight section 58. The electromagneticlaser energy converges at the focal point 52 and then symmetricallydiverges after the focal point 52, which is to the right of the focalpoint 52 in FIG. 2. When the laser energy travels out of the exit 60 theoutlet 28, the diameter of the converged beam 70 is still less than thefluid stream diameter. The total internal reflection of the flow 38 ofthe fluid retains the laser energy within the flow 38 of the fluid afterthe flow 38 travels out of the exit 60 the outlet 28.

While in the depicted exemplary embodiment the focal point 52 issituated near the center of the straight section 58 of outlet 28, thisis intended to be merely one illustration of how the advantageousresults described herein can be obtained and is not intended to belimiting. Alternatively, the outlet 28 could be configured in any of avariety of other fashions, and the focal point could be located at anyof a variety of locations within the flow 38 without departing from thespirit of the instant disclosure. For instance, the focal point 52 couldbe spaced slightly before the entrance 56 the straight section 58, or itcould be situated anywhere along the length of the straight section 58,or the focal point 52 potentially could be somewhere along the free jet64 and after the exit 60, without departing from the present concept.

The collimated laser beam 44 may have a diameter, i.e., width, of ⅜inch, by way of example. The lens 40 converges the collimated laser beam44 through the convergence region 48 until at the focal point 52 theelectromagnetic energy from the laser 8 has a diameter, i.e., width, ofapproximately 1/32 inch, which is approximately 0.8 millimeters. Theexemplary nozzle 32 in the straight section 58 has an internal diameterof approximately 1.0 millimeters. Alternatively, by way of example, theelectromagnetic energy could have a diameter 0.5 millimeters at thefocal point 52 and the nozzle 32 in the straight section 58 could have adiameter of 0.8 millimeters. Other dimensions can be employed.

In the absence of the flow 38 of the fluid, such as if the deliverydevice 4 were instead situated in a vacuum, the electromagnetic energyfrom the laser 8 at a location beyond the focal point 52, i.e., at alocation to the right of the focal point 52 from the perspective of FIG.1, would tend to diverge into a beam of expanding diameter.Advantageously, however, the provision of the flow 38 of the fluidcauses the electromagnetic energy from the laser 8 to instead form aconverged beam 70 downstream, i.e., to the right from the perspective ofFIG. 1, of the focal point 52. The electromagnetic energy enters theflow 38 roughly parallel with columnar axis of the free jet 64 tomaintain a low angle of incidence with surface and thereby enable theinternal reflectivity of the flow 38 to retain the converged beam 70within the interior 74 of the free jet 64. The converged beam 70constitutes substantially all of the electromagnetic energy that wasemitted by the laser 8 in the collimated laser beam 44. The flow 38forms the electromagnetic energy that travels from the focal point 52into the converged beam 70 inasmuch as the flow 38 has a total internalreflectivity that is sufficiently high that the converged beam 70 isretained within an interior 74 of the flow 38.

Such total internal reflectivity is maintained by forming the flow 38 asa columnar flow. As is understood in the relevant art, a fluid streamexhibits Plateau-Rayleigh instability due to fluid surface tension,resulting in fluid thread breakup. This instability places on upperlimit on the distance that the free jet 64 can travel from the nozzle 32while continuing to retain the converged beam 70 within its interior 74.With increased distance from the nozzle 32, surface undulations on thejet 64 eventually become significant enough in size and quantity tocause a reduction in internal reflectivity. It is understood that jet 64will exhibit what is likely its greatest usable length when the nozzle32 is designed to maximize the initial uniformity of the flow 38 intojet 64. A variety of nozzle designs, flow velocities, and distancesbetween the nozzle 32 and the workpiece 12 can be employed so long asthe jet 64 remains sufficiently columnar such that its total internalreflectivity remains sufficiently high to retain enough of the energy ofthe converged beam 70 within the interior 74 of the flow 38 that, forinstance, the laser peening operation is successful.

It thus can be understood that the flow 38 of the fluid functions inmuch the same way as a fiber optic cable, and the converged beam 70 willbe retained within the interior 74 of the flow 38 despite the deflectionof the free jet 64 as a result of gravity acting thereon so long as thediameter of the free jet 64 remains substantially unvarying and the flow38 remains substantially columnar. Typically such a columnar flow willbe laminar, but this need not necessarily be the case.

As noted, the total internal reflectivity of the free jet 64 issufficiently high that it retains the converged beam 70 within theinterior 74 of the free jet 64, and this is at least in part because theindex of refraction of the fluid is greater than the index of refractionof the medium 68. Furthermore, such retention of the converged beam isachieved in part because the converged beam 70 has an angle of incidenceat an internal boundary between the free jet 64 and the medium 68 thatis sufficiently shallow that the converged beam 70 is reflected backinto the interior 74 rather than exiting the free jet 64. Again, theconverged beam 70 is retained within the interior 74 as long as the freejet 64 remains sufficiently columnar. While the exemplary fluiddescribed herein is water, and while the exemplary medium 68 describedherein is air, it is understood that other materials can be employeddepending upon the particular needs of the given application withoutdeparting from the spirit of the present disclosure.

As can further be seen in FIG. 1, the free jet 64 impinges on theworkpiece 12 at a location of impingement 72 thereon. In the depictedexemplary embodiment, the impingement of the converged beam 70 on theworkpiece 12 at the location of impingement 72 performs a laser peeningoperation on the workpiece 12 at the location of impingement 72.Advantageously, the impingement of the free jet 64 itself on theworkpiece 12 at the location of impingement 72 is employed as aninertial blanket for the plasma that is generated by the laser peeningoperation at the location of impingement 72. That is, the fluid of thefree jet 64 impinging on the workpiece 12 provides a fluid cover at thelocation of impingement 72 that retains the plasma by resisting it fromexpanding and traveling away from the workpiece 12 in a directiongenerally toward the delivery device 4. After impingement of the freejet 64 on the workpiece 12 at the location of impingement 72, the freejet 64 fans out, as at the numeral 80, on the surface of the workpiece12 and then form drips as a trickle 78 of fluid that flows verticallydownward on the workpiece 12 due to gravity, as is indicated at thearrow 78. The free jet 64 at the location of impingement 72 contains atthe surface of the workpiece 12 the plasma and the debris that isproduced from the laser peening operation at the location of impingement72, and thus the jet 64 quickly washes away in the trickle 76 of thefluid the plasma bubble and the debris that result from the laserpeening operation. This is advantageous because the rapid cleansing ofthe location of impingement 72 allows for a high repetition rate for thelaser peening shots and improved processing speed. In addition,containment and disposal of the relatively small trickle 76 is fareasier than containing and disposing of a water blanket that covers arelatively much larger area on the workpiece 12. This results in costssavings and simplicity of operation. It thus can be seen that the flow38 of the fluid serves as 1) an optical conduit, 2) an internal coverthat contains the plasma that is formed at the location of impingement72, and 3) a method to wash away the plasma bubble and debris.

Upon impinging on the workpiece 12 at the location of impingement 72,the converged beam 70 that is situated within the interior 74 of thefree jet 64 delivers electromagnetic energy to an area approximatelyequal to or only marginally larger than the incident free jet 64. Sincethe diameter of the free jet 64 does not vary substantially between theexit 60 and the workpiece 12 (which is typically a distance of severalcentimeters), the size of the converged beam 70 incident on theworkpiece 12 at the location of impingement 72 remains of substantiallythe same size and is nearly constant regardless of whether the distanceis two centimeters, three centimeters, or four centimeters, by way ofexample. As such, the distance between the exit 60 and the workpiece 12at the location of impingement 72 can vary generally so long as the freejet 64 remains substantially columnar.

The aforementioned possible variability in the distances between thedelivery device 4 and the workpiece 12 while performing a laser peeningoperation demonstrate that the present concept provides greatflexibility in peening non-planar surfaces in conjunction with the useof a simplified robotic nozzle positioning system upon which thedelivery device 4 is situated. With previous laser peening systems thedistance between the laser and the workpiece was required to be keptvery precise in order to maintain a precise focus of the laser on theworkpiece. The delivery device 4 advantageously avoids the need tomaintain a precise distance between the delivery device 4 and theworkpiece 12 since the focusing of the laser 8 is achieved inside theflow 38, and the flow 38 retains the converged beam 70 therein andimpinges the converged beam 70 on the workpiece wherever the free jet 64impinges. In addition, the free jet 64 dissipates the shock waves thatemanate from the location of impingement 72 and thereby minimizes thepotential for damaging the delivery device 4.

It thus can be seen that the free jet 64 functions both as an opticalconduit for the converged beam 70 as well as a source of water that issufficient to cover the location of impingement 72 and to trap theplasma at such location in order to avoid damage to the delivery device4. The free jet 64 is configured to have a sufficiently low velocity tomaintain a columnar shape with a typically laminar flow characteristic,and the trickle 76 that results from the impingement of the free jet 64at the location of impingement 72 is a relatively small volumetric flowwhich is far smaller in flow rate than a water blanket such aspreviously had been required with prior laser peening operations. Otheradvantages will be apparent.

An improved method in accordance with the disclosed and claimed conceptis depicted in FIG. 3. The method can begin, as at 106, where thedelivery device 4 forms within the medium 68 the flow 38 in the form ofa free jet 64. The fluid that forms the free jet 64 has an index ofrefraction greater than that of the medium 68 within which the free jet64 is formed. The method can then continue, as at 110, where a beam ofelectromagnetic energy, such as the collimated laser beam 44, isreceived within the interior 74 of the flow 38. The method alsoincludes, as at 114, maintaining a total internal reflectivity withinthe interior 74 of the flow 38 sufficient to retain the converged beam70 within the interior 74 of the flow 38.

The method can include performing a laser peening operation at thelocation of impingement 72, although other uses potentially can be madeof the converged beam 70 that is situated within the interior 74 of theflow 38. It is therefore reiterated that the performance of a laserpeening operation using the delivery device 4 is not intended to belimiting. It is also noted that the exemplary laser 8 outputs thecollimated laser beam 44 having a diameter much greater than that of thefree jet 64, and that the lens 40 is therefore provided in order tointensify the collimated laser beam 44 by concentrating its energywithin the relatively smaller converged beam 70. It is understood,however, that other embodiments of the delivery device potentially couldemploy a different delivery mechanism having a laser that outputs acollimated output that is already slightly less than the diameter of thefree jet 64, thereby obviating the need for the lens 40 in such anapplication.

Furthermore, it is noted that the laser 8 typically will be physicallymounted to the delivery device 4, although this need not necessarily bethe case. While the collimated laser beam 44 is depicted in FIG. 1 asbeing oriented parallel with the central axis of the nozzle 32, it isunderstood that in alternative embodiments the laser 8 can be otherwisepositioned and can rely upon mirrors and/or fiber optic devices todirect a beam of electromagnetic energy from such laser into the flow38. It thus is understood that the exemplary delivery mechanism 18 thatis depicted in FIG. 1 is not intended to be limiting in any fashion, andit is understood that any set of components can be provided to deliver abeam of electromagnetic energy into the interior 74 of the flow 38,after which the total internal reflectivity of the flow 38 will retainthe beam of electromagnetic energy within the interior 74.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular embodiments disclosed are meant to be illustrative only andnot limiting as to the scope of the invention which is to be given thefull breadth of the foregoing disclosure.

What is claimed is:
 1. A delivery device comprising: a housing having ahollow cavity formed therein, an inlet in fluid communication with thecavity and structured to deliver a stream of a fluid to the cavity, andan outlet in fluid communication with the cavity and structured todeliver a flow of the fluid out of the cavity, the outlet comprising astraight section, a curved entryway, and a tapered region situatedupstream of the straight section; and a lens having a focal point andthe lens structured to deliver a beam of electromagnetic energy into thefocal point along a length of the straight section.
 2. The deliverydevice of claim 1 wherein the outlet is structured to deliver as theflow a columnar flow of the fluid out of the outlet.
 3. The deliverydevice of claim 2 wherein the outlet is structured to deliver as thecolumnar flow a columnar jet of the fluid out of the outlet.
 4. Thedelivery device of claim 3 wherein the outlet is structured to deliveras the columnar jet a free jet having a total internal reflectivitysufficient to retain the beam within the interior of the free jet. 5.The delivery device of claim 1 wherein the lens is structured to receivethe beam from an emitter and to direct the beam such that a diameter ofthe beam is less than a diameter of the fluid stream.
 6. The deliverydevice of claim 5, wherein the delivery device further comprises theemitter, and wherein the emitter is a laser.
 7. The delivery device ofclaim 1 wherein the straight section has an unvarying diameter.
 8. Thedelivery device of claim 1 wherein the curved entryway is situatedupstream of the tapered region.
 9. A delivery device comprising: ahousing comprising a cavity formed therein, an inlet in fluidcommunication with the cavity and structured to deliver a stream of afluid to the cavity, and an outlet in fluid communication with thecavity and structured to deliver a flow of the fluid out of the cavity,the outlet comprising a straight section, a tapered region situatedupstream of and adjacent to the straight section, a curved entrywaysituated upstream of and adjacent to the tapered region, wherein a firstend of the curved entryway adjacent to the cavity is larger than asecond end of the curved entryway opposite from the first end; and alens structured to deliver a beam of electromagnetic energy out of theoutlet and within the flow.